Okay I need you guys advice on this please

So my boyfriend has never had a job before due to the fact he was pursuing a career in college so he was a full time student, we found out I’m pregnant a few weeks ago & when we found out, he immediately started job searching, fortunately, he got a job interview and hired on the spot! He came to the decision that he was going to put his school on hold for now and focus on earning an income to move us into our own place. As soon as I found out I was pregnant, his mom decided it was best to take me in. Everything here has been great. So about 7 months ago his older sister who is now 30 years old and her whole life she has been lazy, never wanted to get a job & decided to get pregnant willingly for the second time all relying on my boyfriend’s mother. So she moved in here, rent free. So recently she got a job at a day care where they would willingly allow her to bring her 9 year old & her 7 month old child & for some reason she didn’t want them there because she didn’t want them to know she had children (idk??) so for about a week straight she has been coming into me and my boyfriend’s room at 5-6 in the morning and puts her 7 month old in our bed to watch her kids without even asking if it’s okay, she literally just puts her son in our bed and leaves. She is gone from 5-6 in the morning & gets off of work at 5. So the past 3 days she has done this except now she doesn’t come straight home, she goes shopping, gets her nails done, hair done, goes out to eat with her friends before coming home & me and my boyfriend are left here all day long to watch after her 2 children.. no pay at that. We had to buy the baby diapers & formula & have to buy the 9 year old daughter McDonald’s because she doesn’t eat “home cooked meals “ (something her mother got her used to). So yesterday at midnight she had texted my boyfriend for the first time asking him if he could watch them, he said he couldn’t because he possibly started work tomorrow so he wasn’t sure. So she left in the morning and left the kids in her room with the door shut. she didn’t bring the baby to our room like she usually does. Of course, my boyfriend was called into work yesterday so we both left. Apparently, she had left her kids here. We didn’t know because she lives all the way downstairs in the basement and we’re 2 floors above her. We didn’t hear a baby crying, we didn’t hear her daughter who is usually in the living room playing, nor did she text us to tell us the kids were there. About 15 minuets after we left she texted my boyfriend a huge long paragraph saying next time he leaves he should tell her because the kids were here all alone when she got home from work (she lied about being at work, she was on social media posting that she was out with her friends for their birthday and lied that she was at work) and she goes “I bet if I payed you you wouldn’t have had an issue watching them). So my boyfriend left work for this and we came home. She immediately starts cussing at him, saying he’s a piece of shit uncle for leaving the kids alone so she took his cell phone and threw it across the kitchen and it completely took the screen off of the phone and she picked it up and threw it in the trash. After that she bad mouthed me saying I don’t do shit here and the least I could do is watch her kids for her. Keep in mind she doesn’t pay rent, doesn’t put food in the house. She never paid us for watching her kids for 12-16 hours a day, never paid us back for the stuff we had to buy her kids. We honestly aren’t money hungry but we have a child on the way, the money we used is the money I make from my little part time job & we even skipped meals to feed these kids. She receives $900 in cash assistance plus $650 in child support and never kicked out any money to us not even $10 for going out of our way for her. Now my question is how should I go about this? My boyfriend just left to work and her sister is still bad mouthing us. Should I approach her or are we wrong?

Update:

The reason my boyfriend’s mom felt as though it would be best to move me in here with them was because my father is an alcoholic, abusive & smokes weed in front of me, a lot of times him being drunk turns into altercations where he will physically put his hands on me and sometimes he will put me out. So home isn’t a safe environment to be in while pregnant.

Secondly, I can’t get a full time job. My case is a little different. So when I was 14 I was diagnosed with degenerative disk disease as well as 3 disks in my back where replaced with medal ones. I have a liver disorder, which prevents me from being able to take Tylenol as well as anything that had acetaminophen (which is in basically all pain medicine). So I would rely on ibuprofen or sometimes even narcotics because sitting or standing or bending down causes extreme back pain. Now that I’m pregnant I can’t take anything for pain. So, I work a limited amount of hours because I can’t handle it. On top of the back pain for some reason now I swell up in the feet very bad, which gets to the point of almost not being able to walk. So again, I’m trying my best to bring something to the table and I’m pushing myself to my limits.

Thirdly,

Mom is aware of what’s going on, she tells us not to worry about her & to just simply not watch her kids. She tries to be a good mother by giving her advice constantly which always ends in altercations that are very intense. The only reason she won’t put her out of the house now is because she cares for her grandkids and doesn’t want them out on the street.

To add a side note as well.

Her problem with me is mainly because I get to live with my boyfriend here. She expresses this with her mother so this is how I know this. She doesn’t like me and can’t stand my boyfriend (her own brother) because he’s allowed to have me here. She’s upset because mom doesn’t allow her to bring different men here. Might I also add that on weekends and before she started working she would bring men here, tell her 9 year old daughter to go in the other room and watch the baby in the other room while she legitimately sucks dick & has sex so loud everytime you can hear it throughout the house. She’s exposed to this often & when we can we intervene and bring the kids to our room, but she can hear things clearly even in our room. She never disciplined her daughter & her daughter again like I said will only eat outside food like McDonald’s or Burger King. She will literally go on a strike for 2 days without eating if she doesn’t get it. We don’t want her to starve either.

Might I also mention.. she doesn’t clean here. She has never washed a dish, she has never cleaned a countertop. My boyfriend’s mom has insisted we not pay rent because she wants us to save our money for the baby. So because I don’t pay rent, I constantly clean here. I vacuum, clean bathrooms wash dishes and my boyfriend’s mom is extremely grateful for that. His sister doesn’t clean, I’m always cleaning up after her. I do get a little bit of food stamps, so I put food here and cook dinner for the family. When she decides to cook for herself she leaves a mess and food everywhere and I’m left to clean. So again, she’s a shit mom honestly & my boyfriend & I have thought about calling CPS but didn’t want to be “dramatic “.

Oh, and the reason I know her daycare will allow her to bring her children is because she’s told us personally multiple times.

His mom works all day long. She leaves at 6 am and gets home at 11 pm Monday- Saturday so that’s why she doesn’t stay with them.